Say goodbye to the longest bull market for bonds in history. The market is at a turning point, say portfolio managers—some of whom are running the nation’s largest bond funds.

The reason: growing worries about inflation. While it is not a problem right now, there are several strong economic factors that typically lead to higher prices down the road. "Inflation will be higher than they (Federal Reserve policymakers) think," says Mark Zandi, Moody’s Analytics chief economist.

"They said they'll start to raise rates late 2014, but they'll be unable to stick to that commitment," Zandi says. "They'll be under pressure to start tightening sooner."

An improving jobs market, a stronger dollar and rising commodity prices are adding to pricing pressures on everyday goods. As a result, the Fed—mandated to keep inflation in check—could be forced to raise interest rates sooner than expected. Rates are already starting to rise, even without the Fed. This week, Treasurys saw a sharp sell-off, bringing yields —which move opposite to prices—to their highest level since October.

Rising yields, when coupled with inflation, are a double-whammy to the value of bonds.